| 摘要 |
PROBLEM TO BE SOLVED: To reliably withdraw a drilling tool along with a drilling bit even if jamming or the like occurs. SOLUTION: A device 14 is attached to a tip of a rod 13 inserted in a casing pipe 11, and the drilling bit 15 is mounted on a tip of the device 14 so as to be detachable from the device 14. An outer circumference of the tip of the device 14 has projecting portions 27 and engaging portions 27a sectionally projecting beyond the projecting portions 27. An inner circumference of a bore portion 15d formed in a rear end of the drilling bit 15 to enable the insertion of the tip of the device 14 has grooved portions 28 in which the projecting portions 27 and engaging portions 27a can be inserted, and an engaged portion 28a with which the engaging portions 27a can be engaged in the rear end direction on an axis O when the device 14 whose tip is inserted in the bore portion 15d with the projecting portions 27 and engaging portions 27a being inserted in the grooved portions 28 is circumferentially turned about the axis O. COPYRIGHT: (C)2004,JPO
|
